1. Field
The following description relates to a pH-sensitive polymer hydrogel with dual ionic transition and the use thereof.
2. Description of Related Art
In the medical field of drug delivery systems, intensive research has recently been focused on sustained drug delivery of physiologically active agent using the sol-gel transition of a hydrogel made of an amphoteric polymer with both hydrophobic and hydrophilic groups.
U.S. Pat. No. 4,942,035 discloses a copolymer consisting of a hydrophilic polymer, e.g., polyethylene glycol, and a biodegradable polyester, e.g., polylactide, polyglycolide, or polycaprolactone, which surmounts the problem that the block copolymer composed of polyethylene glycol and a polyethyleneoxide-polypropyleneoxide-polyethyleneoxide block copolymer, called Pluronic, is not biodegradable.
U.S. Pat. No. 5,476,909 describes a biodegradable triblock copolymer of an A-B-A type which essentially consists of polylactic acid (PLA), polyglycolic acid (PGA), or PLA/PGA as the hydrophobic block (A), and polyethylene glycol (PEG) or derivatives thereof as the hydrophilic block (B).
Korean Patent Laid-Open Publication No. 2000-0012970 teaches a pH-sensitive polymer comprising a sulfonamide group, and a preparation method thereof, focusing on the solubility of linear polymers prepared by random copolymerization of sulfonamide monomers, and dimethyl acrylamide or isopropyl acrylamide, and on the degree of swelling of the crosslinked polymers.
These conventional techniques concern block copolymers consisting of biodegradable hydrophobic polymers and hydrophilic polymers which exhibit sol-gel transition according to temperature so that after being introduced in a liquid form of sol into the body, the block copolymers experiences phase transition into a gel due to the body temperature, thus acting as a sustained drug delivery system which is stably impregnated with a drug and releases the drug in a sustained manner. However, block copolymers that exhibit sol-gel transition according to temperature suffer from the drawback of clogging the syringe needle before completion of the introduction because they gel in the course of injection as the syringe needle reaches thermal equilibrium with the body temperature. Although reported to be pH-sensitive, the hydrophobic moiety consisting of polylactic acid (PLA), polylactic acid-co-polyglycolic acid (PLGA), polycaprolactone (PCL), or polycaprolactone-co-polylactic acid (PCLA) is not sufficiently sensitive to pH in vivo so that it cannot be applied to drug delivery in practice.